Seismology is used for exploration, archaeological studies, and engineering projects that require geological information. Exploration seismology provides data that, when used in conjunction with other available geophysical, borehole, and geological data, can provide information about the structure and distribution of rock types and their contents. Such information greatly aids searches for water, geothermal reservoirs, and mineral deposits such as hydrocarbons and ores. Most oil companies rely on exploration seismology to select sites in which to drill exploratory oil wells.
Traditional seismology employs artificially generated seismic waves to map subsurface structures. The seismic waves propagate from a source down into the earth and reflect from boundaries between subsurface structures. Surface receivers detect and record reflected seismic waves for later analysis. Though some large-scale structures can often be perceived from a direct examination of the recorded signals, the recorded signals must be processed to remove distortion and reveal finer detail in the subsurface image. The quality of the subsurface image is highly dependent on the accuracy of the subsurface velocity model.
Velocity analysis is the term used to describe the act of extracting velocity information from seismic data. The advanced prestack depth migration technique has become an attractive tool for velocity analysis, not only because of its sensitivity to the velocity model but also its ability to generate residual errors in the post-migration domain. A popular approach to the migration-velocity analysis (MVA) is the residual-curvature analysis on a common image point gather, which is based on residual moveout to measure velocity error. Residual-curvature analysis in areas of complex structure is a coupled migration-inversion problem that can be analyzed from a tomographic perspective. See, e.g.:    Stork, C., and R. W. Clayton, 1991, Linear aspects of tomographic velocity analysis: Geophysics, 56, 483-495.    Stork, C., 1992, Reflection tomography in the postmigrated domain: Geophysics, 57, 680-692.    Liu, Z., 1997, An analytical approach to migration velocity analysis: Geophysics, 62, 1238-1249.    Meng, Z., N. Bleistein, and K. D. Wyatt, 1999, 3D analytical migration velocity analysis I: Two-step velocity estimation by reflector-normal update: 69th Annual International Meeting, SEG, Expanded Abstracts, 1727-1730.    Zhou, H., S. H. Gray, J. Young, D. Pham, and Y. Zhang, 2003, Tomographic residual curvature analysis: The process and its components: 73rd Annual International Meeting, SEG, Expanded Abstracts, 666-669.
Under the limiting assumptions of lateral velocity homogeneity, small dip, or small offset, various approximations were derived to express the velocity updates as a function of offset in a post-migration common image point gather (CIG). In Meng, Z., P. A. Valasek, S. A. Whitney, C. B. Sigler, B. K. Macy, and N. Dan Whitmore, 2004, 3D global tomographic velocity model building: 74th Annual International Meeting, SEG, Expanded Abstracts, 2379-2382, a decoupled tomographic system was developed to address the ambiguity between velocity and depth for velocity update.
The common angle imaging (CAI) framework provides a way to exploit the redundancy in post-migrated seismic data to obtain multi-parameter estimates of subsurface properties. A 1-D velocity updating algorithm based on measured residual moveout on CAI gathers is described in Mosher, C. C., S. Jin, and D. J. Foster, 2001, Migration velocity analysis using common angle image gathers: 71st Annual International Meeting, SEG, Expanded Abstracts, 889-892. In Xia, F., Y. Ren, and S. Jin, 2006, Residual migration-velocity analysis using common angle image gathers: Presented at the 76th Annual International Meeting, SEG, the authors incorporated structural dip information into the interval velocity update and proposed a method for residual migration velocity analysis in the depth-offset ray parameter domain.
Existing seismic data processing methods do not sufficiently remove image distortion, and they continue to require excessively long computation times. Improved systems and methods are disclosed herein.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description are not intended to limit the disclosed embodiments to the particular form shown, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims.